1. Field of the Invention
The present invention generally relates to data processing method/apparatus, data reproducing method/apparatus, and a recording medium. More specifically, the present invention is directed to such data processing/recording methods/apparatuses capable of quickly random-accessing multiplexed program data by extracting feature point information from a coded transport stream.
2. Description of the Related Art
In multi-channel digital television broadcasting systems known as the European DVB (Digital Video Broadcast) system and the Japanese digital BS (Broadcast Satellite) broadcast system, the MPEG (Moving Picture Experts Group)-2 transport stream is used. A transport stream corresponds to such a stream in which a transport packet is continued. A transport packet corresponds to such a packet that, for instance, either an MPEG-2 video stream or an MPEG-1 audio stream is packeted. Either one program or a plurality of AV (Audio Visual) programs are multiplexed on a single transport stream which is transmitted by way of broadcasting electromagnetic waves. In general, AV programs of each channel are independently provided from each other.
As a consequence, when a transport stream transmitted in a broadcasting channel is directly received and then recorded by a home-use receiver, AV programs of all channels contained in this transmitted transport stream may be recorded at the same time. Also, when transport streams of AV programs of several channels selected from this broadcasted transport stream by a user are separated and then recorded, AV programs of an arbitrarily selected channel may be recorded at the same time.
FIG. 1 indicates an example of one conventional transport stream recording method. FIG. 1A shows such a transport stream on which a plurality of AV programs is multiplexed. In this drawing, an abscissa shows time. This time is segmented every time unit TUi (i=0, 1, 2, - - - ) having an interval “Δt”. Either one AV program or a plurality of AV programs are selected from an input transport stream. The selected transport packets are indicated by using hatched lines. Generally speaking, as shown in FIG. 1B, these selected transport packets will appear at irregular timing, and thus, a total number of transport packets every time unit TUi is changed.
As indicated in FIG. 2, the transport packets which are selected every such a time unit TUi having the interval of Δt are recorded on a recording medium, while the intervals are shortened. At this time, these transport packets are recorded on this recording medium, while adding thereto time stamps indicative of time instants on the respective transport streams. This time stamp is similar to such a TSP_extra_header having a length of 4 bytes. That is, this 4-byte TSP_extra_header is added to the transport packet which is defined in, for instance, the DV (Digital Video) format (Specification Of Consumer-Use Digital VCRs using 6.3 mm magnetic tape in HD digital VCR conference), and PART7-DVB Specifications of Consumer-Use Digital VCR).
In FIG. 2, an abscissa indicates an address representative of a byte position of a recorded transport stream. When the transport stream having the variable bit rate shown in FIG. 1B is entered, a recording apparatus inserts dummy data into this input transport stream, and then records the resulting data at a fixed recording rate, as indicated in FIG. 2. As a consequence, a data amount with respect to a time elapse of the recorded transport stream may have a direct proportional relationship. In other words, assuming now that an amount of recorded data per a time unit is selected to be “x”, a byte position of head data of an n-th (n=0, 1, 2 - - - ) time unit is equal to such a position obtained by multiplying x by n.
In this recording method, since the dummy data is inserted into the transport streams so as to achieve a constant recording rate, the recording efficiency of the transport stream is not so high. However, if such dummy data is not inserted, then the time elapses of the recorded transport streams is no longer directly proportional to the data amount of the file. As a result, in the case that such data located at a desired position on the time axis of the transport stream is accessed, there is a problem that the data access characteristic would be deteriorated.
Also, generally speaking, in an MPEG-2 video data stream, I picture are coded in an interval of approximately 0.5 seconds, and other pictures are coded as either P pictures or B pictures. As a consequence, when a video signal is reproduced in a high speed from a recording medium on which the MPEG-2 video data streams are recorded, such I pictures must be searched. However, in the case that the I pictures are reproduced by way of the random access manner from the recording medium on which the transport streams such as the digital broadcasting system are recorded, it is practically difficult to search the starting bytes of the I pictures in higher efficiencies. In other words, the syntax of the video streams which are read from the random byte positions of the transport streams recorded on the recording medium is analyzed, and thus, the starting bytes of either the I pictures or the audio frames are searched. As a consequence, lengthy search time of the I pictures is required in the worst case. Also, the high-speed random access reproducing operation cannot be carried out in response to the user input.